leandrocp mdex up to 0.13.1 Normalization delta_converter.ex Delta cross site scripting

Summaryinfo

A vulnerability classified as problematic has been found in leandrocp mdex up to 0.13.1. This affects an unknown part in the library lib/mdex/delta_converter.ex of the component Normalization Handler. This manipulation of the argument Delta causes cross site scripting. This vulnerability is registered as CVE-2026-54889. Remote exploitation of the attack is possible. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in leandrocp mdex up to 0.13.1. It has been declared as problematic. Affected by this vulnerability is some unknown processing in the library lib/mdex/delta_converter.ex of the component Normalization Handler. The manipulation of the argument Delta with an unknown input leads to a cross site scripting vulnerability. The CWE definition for the vulnerability is CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. As an impact it is known to affect integrity. The summary by CVE is:

Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in leandrocp mdex allows cross-site scripting via unsanitized URL schemes in Quill Delta output. 'Elixir.MDEx':to_delta/2 converts Markdown into a Quill Delta. 'Elixir.MDEx.DeltaConverter':default_convert_node/3 in lib/mdex/delta_converter.ex copies the URL of a link, wikilink, or image node directly from the parsed Markdown into the Delta "link" or "image" attribute without applying a scheme allowlist or any normalization. An attacker who controls the Markdown text can supply a javascript: URL (for example [click](javascript:alert(document.cookie))) that survives verbatim into the Delta attribute. When the Delta is rendered to HTML by a downstream renderer (such as quill-delta-to-html or the Quill client), the attribute becomes an or , and the javascript: scheme executes in the browser of anyone who views the rendered content. The link and wikilink cases are the strongest vectors because javascript: in an href executes on click; the image case is lower impact because javascript: in generally does not execute in modern browsers. This issue affects mdex: from 0.8.3 before 0.13.2.

The weakness was published by Peter Ullrich and Jonatan Männchen as GHSA-4383-7xfp-gpph. It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-54889 since 06/16/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

Upgrading to version 0.13.2 eliminates this vulnerability. Applying the patch 2817147f5b87ce7186aa604c9ee72499485b8f2f is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• leandrocp

Name

• mdex

Version

• 0.13.0
• 0.13.1

License

• open-source

Website

• Product: https://github.com/leandrocp/mdex/

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